1. Field of the Invention
The present invention relates to a ball point pen filled with an erasable ink lines drawn with which can be erased with an eraser.
2. Description of the Related Art
Conventional ball point pens filled with an ink which is erasable with an eraser have been materialized by providing an ink with such very high viscosity as one million to 600 million mPa.s by using a pigment as a colorant in combination with a rubber-like material in order to make written letters erasable.
Such a method has had a disadvantage that a writing feeling is not smooth and drawn lines have a low intensity because of inferior flow of the ink.
In trying to simply solve this disadvantage, it would be considered that the viscosity of an ink is to be lowered to improve the flow of the ink. However, a reduction in the viscosity of the ink causes the ink to easily permeate into paper and brings about a disadvantage that the erasability of the written letters is notably degraded.
Accordingly, in order to solve these disadvantages, proposed is a ball point pen ink prepared by adding at least one of an inorganic compound which has a fine particle diameter and is inert to the ink component, a semi-solid material and a soft solid material having a melting point of 130.degree. C. or lower, to an ink composition which comprises a rubber component, a volatile solvent dissolving the rubber component, a non-volatile solvent which does not dissolve the rubber component and a pigment.
In writing, this ink has such a relatively low ink viscosity that an outflow of the ink has been able to be improved much. The volatile solvent contained in the ink composition is volatilized after writing to cause the ink to reach a very high viscosity, whereby the ink is prevented from permeating into paper, and thus the ink has become erasable though not to the sufficient extent. Used as a volatile solvent are aliphatic hydrocarbons such as n-hexane, n-heptane, n-octane and isohexane, petroleum base solvents such as solvent naphtha, heavy naphtha, kerosene and ligroin, aromatic hydrocarbons such as benzene, xylene and toluene, and mixed solvents thereof. Plasticizers such as DOP, DOA and DBP are used as a main component for the non-volatile solvent. These solvents are very harmful to a human body. In general, non-polar solvents are mainly used as a solvent for this ink in order to dissolve a rubber component and have a low surface tension.
This causes a part of the ink to quickly permeate into paper before volatilizing. The ink which has once permeated can not easily be erased with an eraser. Therefore, the ink has a disadvantage that the erasability is unsatisfactory.
In addition thereto, erasable inks for a ball point pen having various compositions are proposed, but the current situation is that they have an unsatisfied erasability and desired effects have not yet come to be obtained.